DHCPv6 PD & Routing Questions

Owen DeLong owen at delong.com
Sat Nov 21 01:27:43 UTC 2015

> On 2015-11-20 15:36, Owen DeLong wrote:
>>> On Nov 20, 2015, at 13:35 , Jim Burwell <jimb at jsbc.cc> wrote:
>>> Hi,
>>> Have a simple couple of questions here. 
>>> In my admittedly cursory glances over the DHCPv6 RFCs, I don't see any
>>> reference to the protocol having any role in managing the routing of
>>> prefixes it delegates.  Perhaps I missed it, but I somewhat expected the
>>> omission of this responsibility would be the case.
>>> My questions are:
>>> 1) Does the DHCPv6 protocol include any standards/mechanisms/methods for
>>> managing routes to prefixes it delegates, or does it consider this
>>> outside of its function?  (I suspect the latter)
>> Yes and no…
>> DHCPv6 doesn’t include anything specifically per se, but it does require that
>> the local router sees the DHCPv6 PD answer in the process of passing it
>> along to the target, and there’s a pretty obvious expectation that said router
>> will have to arrange to do the needful in that respect.
>>> 2) What are the most common ways of managing the routing of delegated
>>> prefixes in the ISPs routing domain?  Has a standard method/best
>>> practice emerged yet?  Routing protocols?  IPv6 RAs?
>> RAs really only apply to subnet local advertisement of routers and
>> the on-net prefixes in most implementations.
>> I don’t think any of the various methods of using routing protocols,
>> static pre-routed blocks from which PDs are delegated, etc.  could
>> necessarily be called “standardized”, but there are probably a few
>> that are more popular than most of the others.
>> Unfortunately, PD is really still in its infancy in terms of development
>> and real running code for complete implementations throughout any
>> sort of site hierarchy.
>> Owen
> Thanks for the answer Owen!
> So it sounds like things are still in flux.  But it least it answers my
> main question of "have I missed something here"?
> Could you elaborate on the "local router seeing the PD answer" a bit?  I
> presume by "local router" you mean router acting as DHCPv6 relay?  Or do
> you mean the router which made the original request?

I mean the router that will deliver the PD to the requesting DHCPv6 client.

If the DHCPv6 server is on-net, then this will be the requesting client.
Otherwise, it will be the last relay router.

> Would it be fair to say that the RFCs only really talk about delegating
> the prefixes, and leave what to do with the prefixes themselves up to
> the implementer?

Yes… At least at this time. Some of the work in homenet might include
some suggestions for some implementations.

> I'm asking these questions because I'm doing a little class for some
> folks on IPv6 and this is one area where I couldn't find answers. 

Depending on your audience, I’d suggest that unless this is an advanced
IPv6 class, it’s probably one of those topics left for extra-curicular research.


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